Topic 4

What is the difference between somatic and germ cells

Somatic cells are diploid non‑reproductive cells with 46 chromosomes; germ cells are haploid reproductive cells with 23 chromosomes.

What are the phases of the cell cycle

G0 (rest), G1 (growth and organelle duplication), S (DNA replication), G2 (final protein synthesis), and mitosis or meiosis.

What happens during G0

The cell performs normal functions and is not preparing to divide.

What happens during G1

The cell grows, synthesizes proteins, and duplicates organelles.

What happens during S phase

DNA replication occurs.

What happens during G2

Final protein synthesis occurs before division.

What is mitosis

Division of nuclear material in somatic cells producing two diploid daughter cells.

What are the phases of mitosis

Prophase, metaphase, anaphase, and telophase.

What is meiosis

Division of germ cells producing four genetically unique haploid daughter cells.

What are the phases of meiosis

Prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II.

What is cytokinesis

Division of the cytoplasm following nuclear division.

What are the two primary factors contributing to genetic diversity in meiosis

Crossing over during prophase I and random assortment during anaphase I.

What occurs during Stage 1 of development

Fertilization forms a diploid zygote.

What occurs during Stage 2 of development

Mitotic divisions produce a morula.

What occurs during Stage 3 of development

The morula becomes a blastocyst with embryoblast and trophoblast cells.

What occurs during Stage 4 of development

Trophoblast cells begin implantation by digesting the uterine lining.

What occurs during Stage 5 of development

Implantation completes and the blastocyst becomes an embryo.

What occurs during Stage 6 of development

A primitive streak forms, establishing the cranial‑caudal axis; early blood vessels appear.

What occurs during Stage 7 of development

Gastrulation forms ectoderm, mesoderm, and endoderm.

What occurs during Stage 8 of development

Neurulation begins and the neural tube starts forming.

What occurs during Stage 9 of development

Somites appear and will form vertebrae and muscles.

What occurs during Stage 10 of development

The primitive heart tube fuses and begins early contraction; eye and ear cells appear.

What occurs during Stage 11 of development

The primitive heart tube begins beating.

What occurs during Stage 12 of development

Neural tube closure completes; limb buds appear; early organ differentiation begins.

What is a zygote

A diploid cell formed by fusion of sperm and ovum.

What is a morula

A solid ball of cells formed by mitotic division of the zygote.

What is a blastocyst

A hollow structure with embryoblast and trophoblast cells capable of implantation.

What is an embryo

The developing organism from implantation until Week 9.

What is a fetus

The developing organism from Week 9 until birth.

What is the embryoblast

The inner cell mass that forms the embryo.

What is the trophoblast

The outer cell layer that forms the placenta and mediates implantation.

What is implantation

The process where trophoblast cells digest the endometrium to embed the blastocyst.

What is the primitive streak

A linear thickening that establishes the head‑to‑tail axis and allows cell migration.

What is gastrulation

Formation of the three germ layers: ectoderm, mesoderm, and endoderm.

What is neurulation

Formation of the neural tube from ectoderm, giving rise to the brain and spinal cord.

What is a somite

A paired mesodermal structure that forms vertebrae and skeletal muscles.

What are the three germ layers

Ectoderm, mesoderm, and endoderm.

What does the ectoderm form

The nervous system and outer layer of skin.

What does the mesoderm form

Heart, circulatory system, kidneys, bones, muscles, and connective tissue.

What does the endoderm form

Respiratory system, gastrointestinal tract, liver, pancreas, and thyroid.

What general changes occur during fetal development

Rapid growth, movement, reflexes, heartbeat detection, organ maturation, urine formation, swallowing, and eventual viability by Week 26.